I'm not sure what's causing the ncurses artifacts, as it's not constant as can be seen by the attached pictures and screenshots. First, the issue happens in both X and TTY so I don't think it's just an X issue. I have two instances of Slackware (14.2 on a Lenovo Thinkpad T420 and -current on a desktop) and the issue doesn't happen on the laptop. I'm hoping it's maybe some minor configuration issue and I missed it somewhere.

Here are the artifacts, a picture of Slackpkg in TTY and X on Konsole.
Here's the picture of Slackpkg in TTY
https://imgur.com/BteSouC
Here's a screenshot of Slackpkg in X
https://imgur.com/6GUcWb7

Here are some ncurses screenshots without artifacts
SBOpkg (in TTY)
https://imgur.com/oWM2gBu
nmtui (in X)
https://imgur.com/8CRak6Q

If it helps the desktop is using an AMD Radeon RX550 graphics card with open source drivers, and the installed kernel version is 4.19.39.

Edit: It's worth noting, that everything does work. It just looks bad, and I'd like to figure out why

Hello,

dialog uses ANSI escape sequences to draw the borders.

Probably the font in use is not consistent with your locale.

Using UTF-8 everywhere is better, both in the TTY and under X.

Thanks for the reply, I set 'append="vt.default_utf8=1" ' in /etc/lilo.conf which seems to have fixed the artifacts in TTY.

This makes me think that it's definitely a UTF-8 issue. Unfortunately they're still present in X, I tried several different terminals (URxvt, UXterm, and Konsole) and all of them have the issue.
I tried changing the terminal font and according to at least the settings in Konsole I am using UTF-8 encoding.
I also made sure that /etc/profile.d/lang.sh has 'export LANG=en_US.UTF-8'.

Is there something lower level for X I'm missing? Maybe a font you'd recommend trying?

I use a monospace font.


I can't check the dialog of slackpkg+ that I don't use., but maybe it has some specific settings when running dialog?